(Meth)acrylic acid is generally prepared by gas phase oxidation of propane, propylene, (meth)acrolein, and the like in the presence of a catalyst. For example, propane, propylene, and the like are converted to (meth)acrylic acid through (meth)acrolein by gas phase oxidation in the presence of an appropriate catalyst in a reactor, and a reaction product mixed gas including (meth)acrylic acid, non-reacted propane or propylene, (meth)acrolein, an inert gas, carbon dioxide, water vapor, and various organic by-products (acetic acid, heavies, and the like) is obtained in the back end of the reactor.
The (meth)acrylic acid-containing mixed gas contacts an absorption solvent including water in a (meth)acrylic acid absorption tower, and is recovered as a (meth)acrylic acid aqueous solution. Further, (meth)acrylic acid-stripped insoluble gas is recycled for a synthesis reaction of (meth)acrylic acid, and a part thereof is incinerated, converted into harmless gas, and discharged. The (meth)acrylic acid aqueous solution is extracted, distilled, and purified to obtain (meth)acrylic acid.
Meanwhile, various methods of controlling process conditions or a process sequence and the like to improve the recovery efficiency of (meth)acrylic acid have been suggested. Representatively, as a method for separating water and acetic acid from the (meth)acrylic acid aqueous solution obtained in the (meth)acrylic acid absorption tower, an azeotropic distillation method using a hydrophobic solvent in a distillation column is known. Further, a method of supplying a (meth)acrylic acid aqueous solution to an extraction column to obtain a (meth)acrylic acid extract solution with reduced water content and a raffinate solution thereof, and distilling the extract, thereby reducing energy consumption amount, is known.
Meanwhile, in the (meth)acrylic acid aqueous solution obtained in the (meth)acrylic acid absorption tower, in addition to (meth)acrylic acid, various organic by-products such as maleic acid, terephthalic acid, aldehyde, and (meth)acrylic acid polymer are included. Further, due to the properties of a continuous process for recovering (meth)acrylic acid, scum is formed due to poorly water-soluble materials in the organic by-products. The scum contaminates a (meth)acrylic acid recovery apparatus, and is particularly accumulated in an extraction column to lower recovery efficiency of (meth)acrylic acid, rendering long-time operation of the continuous process impossible.
Due to the properties of a continuous process, a possibility that solvents used in a (meth)acrylic acid extraction process and a distillation process or the organic by-products may be introduced into a (meth)acrylic acid absorption process or a (meth)acrylic acid synthesis process may not be excluded. Particularly, if the solvents or organic by-products are introduced into a (meth)acrylic acid synthesis process, a reactor and catalyst may be contaminated to lower reaction efficiency, and a serious stability problem may be caused.